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I have done some machine language programming and some of the other higherlevel programming. I think I have a good understanding of how computers work. Does aladder logic symbol relate to a specific routine in the PLC? I have a PLC I am trying to learn to programm and ladder logic is not making a lotof sense. I hope some one here can point me in a direction of a good tutorial, a bookor a web site. thanks

I tend to think of my PLC's differently. There is no real way to do what you want with ladder logic. It's easier to accomplish with a function as an output in ladder logic.

Ladder logic deals primarily with solid state. A device is either ON or OFF. A switch is either OPEN or CLOSED. Each device, say for example a light bulb, has a number of things that have to happen to turn on. Switch 1 may need to be open, Switch 2 may need to be closed and either Switch 3 or Switch 4 must be closed. It relatively easy in ladder logic to perform this.

Wher Tri-Logic comes in is that instead of turning on a light with all those switches, you can turn on a BASIC program that will run and perform your functions.

In your case, a function output would be controlled by inputs called "E-Stop Pressed" AND "Light Curtain Clear" AND "Start Button Pressed". When all three of those events happened at the same time, a function (Output) would be run to pulse your steppers incrementing or decrementing your X and Y values to make your pattern.

The challenge is not really in the Ladder Logic, but in the BASIC function!